Ongoing studies in mice with a double recombinant vaccinia virus vector which expresses antigens from herpes simplex virus (HSV) and influenza A virus have demonstrated that vaccination with the double recombinant provides protection against challenge with either HSV or influenza A comparable to protection provided by respective single recombinants. In addition, vaccination with the double recombinant is not adversely affected by previous immunity to HSV or influenza virus. These findings support further research and development of polyvalent live recombinant vectors as vaccines for immunizing against multiple disease with single vaccination. Clinical studies examining the ability of acyclovir to prevent ultraviolet light-induced reactivation of HSV have continued and a new study examining the ability of sun-blocking agents to prevent ultraviolet light-induced reactivation of HSV was started. A trial to determine the efficacy of daily oral acyclovir in preventing herpes labialis has progressed into the treatment phase of the study. Prior studies with lactate dehydrogenase virus have indicated that impairment of enzyme clearance is an important factor in the regulation of serum enzyme levels. A critical step in the clearance of serum enzyme is the binding of enzymes to macrophages. Studies over the past year have demonstrated that this process can be studied using flow cytometry and that this technique can be used to study the binding of enzymes to cells, identify the cell type to which the enzyme binds and measure changes in the capacity of cells to bind enzymes.